


Omegaverse sheithcest

by alchemist17



Category: Voltron: Legendary Defender
Genre: Alpha Shiro (Voltron), First Time, Keith & Shiro (Voltron) are Siblings, M/M, Non-Traditional Alpha/Beta/Omega Dynamics, Omega Keith (Voltron), Penis In Vagina Sex, Pregnancy Kink, Sibling Incest, Vaginal Fingering
Language: English
Status: Completed
Published: 2019-12-23
Updated: 2019-12-23
Packaged: 2021-02-24 16:34:44
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,668
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21921022
Author URL: https://archiveofourown.org/users/alchemist17/pseuds/alchemist17
Summary: Keith has his first heat early. Luckily his big brother Takashi is home to with him while their parents are away.
Relationships: Keith/Shiro (Voltron)
Comments: 4
Kudos: 188





	Omegaverse sheithcest

**Author's Note:**

> Sorry for the uncreative title but honestly fuck coming up with one  
> And why isn't breeding kink a tag com'on guys?  
> Also I genuinely cannot remember if I intended for Keith to be underage when I wrote this it's so long ago now

"Takashi…" 

"Morning Keith." Shiro says absently, more focused on pouring out the pancake batter.

"I don't feel good."

"Yeah?" Shiro turns around. "Oh, Keith, is-is it your heat?" 

Keith nods miserably. "I think so."

He's visibly sweating, the armpits and neckline of his shirt soaked. There's a damp patch between his legs, spreading down his thighs.

"Did mum get anything ready?" 

"We weren't expecting it for a while yet." He starts to rifle through their medicine box. "I don't think we have anything."

"Takashiiiiii."

"Don't worry. I'll go into town and get something." Shiro turns off the stove, grabs his car keys and the bank card their parents had left for takeaway and emergencies. He's pretty sure Keith going into heat six months early is an emergency. 

Keith whines.

"I know you don't want to be alone but I need to try and get you help." Shiro cups his face and the omega nuzzles his hands fondly. "Uh, why don't you wait in my bed? My sheets, the scent-they'll help calm you."

“I’ll be back as soon as I can. You’re gonna be okay.”

  
  


“What do you mean you don’t have anything?!"

“I’m sorry, it’s just not the right time of year for heat.”

“I know, I know.” Shiro rests his head in his hands.

“I’ll have a look out back, see if there’s anything left.” The pharmacist says kindly.

Shiro desperately searches the internet while she’s gone. But it’s already Friday, nowhere will ship until Monday and Keith needs help now.

“We’ve got this.”

Shiro baulks. “It’s huge!”

“It...definitely isn’t made for beginners. But it’s all we’ve got.”

“Jeez. Okay, I’ll take it. Will he need lube?”

“I don’t suppose you checked how slick he was before you left, did you?”

“Of course not!”

“You should get lube. Young, unmated omegas don’t always get aroused enough for penetration.”

"Okay, I'll get whatever you recommend."

Shiro arrives home with the biggest dispenser of lube he's ever seen. 

"Keith?" 

"Takashi!" comes the reply. 

Shiro grabs water and cereal bars as he passes through the house, knocks tentatively on his bedroom door. 

"I'm gonna open the door a crack and put a bag in for you."

His mouth waters with the scent that wafts out and he feels himself harden instinctively. There's rustling on the other side of the door as Keith opens the bag. 

"Takashi, what the fuck is this?" 

"Language, Keith. And I'm sorry, it's all they had. It's out of season."

"I'm a freak."

“Keith, you’re not a freak. I presented early too, we should of been ready.”

“Everyone will know. They’ll think I’m stupid. Too slutty to wait.”

“The other kids, they-they said the same sort of thing about me. That I was dumb and I didn’t care about anything other than, y’know. It’s tough, but they’ll forget.”

“Does anyone remember yours?” Keith’s voice is a little more distant as he moves to the bed.

“Matt remembers. But he knows it’s a delicate issue so if he brings it up, it means the joke is really funny.” 

Shiro's desperate that know what's happening in there. He sits with his back to the door, his cock is hard in his shorts. It twitches when the nearby omega whines. 

He shakes his head. He can't think of Keith as an omega, he mustn't. Keith's his brother, and he needs Shiro's help. 

"Takashi!" 

"Bab-Keith. Keith, are you okay?"

"It won't fit."

A dark part of Shiro is disappointed. If Keith can't take the dildo, he'll never manage Shiro's cock. 

"I'm sorry. It was all they had." He says again. 

"C-can you come in? Maybe you could just h-hold me?" 

He thinks of how he'd like to hold Keith, hands tight on his hips, on his slim thighs, one hand around both wrists.

"Sure." Shiro says. 

The room is dark. It stinks of fresh omega, and he feels his cock leak onto his pants. Keith is curled among Shiro's rumpled sheets, clutching at his pyjamas. He's naked, skin glistening with sweat and slick.

"Takashiii…"

Shiro darts for the bed. "I'm here baby."

Keith whines at the name. "Please."

Shiro crawls up the bed between his brother and the wall, lays down on the damp sheets. He can feel Keith's heat radiating out. He starts by putting his hand on Keith's upper arm.

"Shit, you're burning. Do you want a fan?" 

Keith shakes his head. He scoots back against his chest, drags his hand round to rest on his stomach.

"Just hold me." He sounds so tired, and Shiro can't help but squeeze him. 

Keith coos happily.

“Does that feel better?”

He nods, and Shiro almost forgets their situation. Until Keith reaches down to pick up the dildo resting on the bed. Shiro tenses.

“Is-is it okay if I try again?” Keith asks. His voice is quiet, unsure.

“S-sure.”

“I feel a little more relaxed now. I was hoping it might fit.”

“It’s okay, try again if you want.”

Keith shifts, hooks his leg back over Shiro’s. His fingertips dig into Keith’s stomach before he relaxes. 

"I-I don't know what to do…" 

Shiro internally curses. He doesn't really know either, other than what he's seen in the alpha marketed porn he watches.

"Just uh, take it slow. Listen to your body."

Keith shakes his head. "Shouldn't listen to body." He says quietly. 

"R-run the head between your legs and push, maybe you'll just uh, let it in? Be gentle, it shouldn't hurt."

"I think I found the hole but-ah!"

He squeezes Keith protectively. "Don't hurt yourself. T-try changing the angle?"

This time, the head of the dildo sinks inside.

"Oooooooh."

"Keith, are you okay?"

"It's-it's inside me."

"How does it feel?" 

"It's big. And it kinda hurts, I think. I'm not sure."

"Just give yourself a moment to adjust. You can do it." Shiro finds his hand is rubbing soothing circles on his belly, instinctively calming the omega. 

Keith sighs as his hole relaxes, the dildo slipping a little deeper. 

"That's it. You're doing great."

Keith shudders in his arms as he clenches at the words.

“Just keep breathing, keep breathing. You’ll be okay.”

He pushes it as deep as it'll go, with two inches still outside of him.

"It already feels so much better."

"That's good, good boy."

"Takashi. Ah…"

Shiro's hand automatically slips lower, his hand easily covering Keith's mound. 

"Feels good." Keith's small hand lays on top of his, and Shiro's trapped.

He's so close to touching Keith properly. He can barely stand it, especially when Keith starts to move the dildo. Shiro almost thinks he can feel the dildo distending Keith's soft skin. He squeezes his eyes shut and bites his lip as Keith squirms. 

"Fuck, this feels good." His nails dig into Shiro's hand. "I never thought it'd feel so good."

Shiro’s shuddery breath tickles his ear.

“You’d never touched yourself before?” Shiro asks. 

Keith shakes his head. "Not… Not inside. I never bothered because it didn't feel like much."

"I guess you just weren't ready yet." Shiro can't help but imagine in, Keith playing with his hole, getting increasingly frustrated until he gives up and touches his clit instead. He could make Keith come from having his pussy played with. He knows he could. 

Keith huffs, let's his arm drop to the mattress. 

"What's wrong baby, why'd you stop?" 

"My arm is tired."

As Keith had hoped, his brother's arm lowers between his legs. He grabs the base of the dildo.

"I'm here. I've got you."

He's slow when he pulls the dildo out, slow enough for Keith's breathing to pick up at the threat of being empty. Shiro eases the dildo back in, the glide sinfully smooth with Keith's slick. Keith's hips push back into his stomach.

It's nothing like the frantic pace Keith had used, and it makes his toes curl at the thought of how Shiro would fuck him. He presses deep, pushes his limits. 

Keith gasps. 

"Is this okay?" Shiro nuzzles at his neck, kisses behind his ear. “I’m not being too rough, am I?”

“You could never be.”

“God, baby…”

Keith's chest heaves as Shiro keeps fucking him with the dildo, firm and slow, just the way an alpha would take him. 

"Taka…" 

"Keith?" 

"Will you knot me?" 

"Keith, baby, we shouldn't. You're too young. A-and you're my brother." Shiro stutters, losing his rhythm. 

"It hurts."

" _ Keith _ ."

"It hurts so bad, I need you to help me." Keith's small hand grabs at his on the dildo, speeding him up. "I always wanted it to be you."

Shiro groans. He's always dreamt of taking Keith's virginity, soothing his pain with his cock and his kisses.

"I could get in trouble if anyone found out. They'd make me go away."

"I promise I won't tell Takashi, please. I'll do anything." Keith turns in his arms, presses a tentative kiss-his first-to Shiro's lips. "I know you'll make it so good for me."

"Baby. You know I can't say no to you."

"You'll do it?" 

"For you."

Shiro cups his face to kiss him. "Just let me get a condom."

Keith whines.

"Baby-"

"No, I understand. I just hate the thought."

"Me too. But we can see about getting birth control for your next heat, and who knows? Maybe someday we could… I mean, if you want, you don't have to."

"Taka, I'm not sure, but I think I'd love to. But maybe we can just talk about it today? I… I like it." Keith mumbles. 

Shiro's hand moves down his body, cups his ass to scoop him closer. "You want me to talk about how fertile you are, how young and sweet your body is?" He can't get much of a grip in the dildo, but he manages to apply pressure to the base, grinds it into him. 

Keith gasps. "Takashi...Please."

"I can't wait to send you out into the world full of pups. For everyone to know you're mine."

"Please, Taka, I need you, fuck, fuck, ah-!"

"Baby." Shiro murmurs, dark and indulgent as his brother shakes in his arms. 

He's boneless, and the orgasm will have helped him stretch. Shiro nudges his thighs open and is about to pull the dildo out when Keith snores in his ear. Shiro rolls his eyes, but presses a fond kiss to his forehead. 

He pulls some of the sweaty sheets over Keith's back and settles down to sleep.

"Takashi…"

Shiro stirs. The soft whimpers continue. His leg is wet. Keith crawls higher up his chest, kisses his mouth. 

"Takashi, you promised."

"Keith."

"Taka."

Shiro's hand has fallen to the bed. He moves it to cup Keith's ass, finds it moving as he grinds his clit against his leg.

"Are you sure this is what you want?"

His fingers slide to press on the base of the dildo, letting Keith push back onto it.

"I'm sure. The dildo just doesn't feel right."

"You seem to be enjoying it."

Keith whines. He knows it's mean to tease but he sounds so sweet. But Shiro's never been able to say no to him. 

"Just let me get a condom on." He grabs one from his drawer, watches Keith frown.

"Why do you have those?" Keith sits up on his knees, high so the base of the dildo doesn't touch the bed.

"So I don't make a mess when I'm in rut."

"You haven't fucked anyone, have you?" 

Shiro rubs the back of his neck. "I've fooled around with a couple betas... But you're my first omega, baby."

Keith pouts.

"I'm sorry baby… I couldn't of known you'd want me. I won't sleep with anyone else now."

"R-really?"

Shiro takes his hand and kisses it. "Just you. Now lie down."

Keith obeys, and Shiro takes a moment to admire him. His body is flushed red in large, uneven patches, and his stomach is concave between his hips. Shiro lays his hand there, and thinks of the day it might swell with his child.

"Alright baby. I'm gonna take the dildo out now.”

Keith's back arches as it slides out, and he tries to cuddle closer once he's empty. Shiro grabs his hips, rolls Keith on top of him. 

"You go on top so you can control the pace. I don't want to hurt you."

The slide of Keith's wet, open pussy is luxurious on his cock. Keith climbs onto his knees, keeps his chest pressed against Shiro's. Shiro holds the base of his cock with one hand, feels blindly for Keith's hole to line them up. 

He pushes back just a fraction, and the head slips in easily.

"Fuck."

"Baby?" Shiro asks softly. He brushes his hair back, tries to look at his face. "Keith, are you okay?"

"Yeah, yeah. You're just… Different."

Shiro's cock twitches, proud at being better than the dildo.

Keith edges backwards, mouth open and panting, drooling on his brother's chest as he takes his first cock.

"There's no rush sweetheart, take all the time you need." His hand moves from his cock to Keith's thigh, grip gentle. 

"C-can you touch my hole?" 

Shiro's hand slides over, fingers splitting smoothly either side of his cock. He rubs his fingers over Keith's stretched labia. Keith pushes back a little more and Shiro chokes on his breath as he feels his cock slide into him.

"You feel so good." He murmurs. His hand smooths up and down Keith's back. "Such a good boy."

"Takashi," Keith whines. "you're so warm inside me."

"You're so beautiful. You look so pretty like this. I love you so much."

"I love you too." Keith pushes back as far as he can, until the extra width of Shiro's knot stops him. 

"How do you feel?" He cups Keith's face in his hands, guides him into making eye contact. 

Keith blinks at him, eyes glazed. "I feel a little better. But-but not too much, I still need you to knot me."

"Don't worry, I'm not going anywhere. You've got me."

"Alpha…"

The name makes Shiro burn. He wraps his arms around his brother and rolls them carefully, until he's got Keith caged beneath him on the bed. 

Keith relaxes into the bed, arches his back and bares his neck temptingly. One of his hands slides down to his stomach. 

"Please Takashi." He whines. "I'm so empty. You're the only one who can fix it."

"I'm here baby."

"But I want you here." Keith stresses, holding his stomach.

"Oh fuck. Someday. Someday I'll breed you up, you'll be full of me and perfect."

"Full of us. Full with our child."

Shiro presses their foreheads together, overwhelmed with emotion. He stares into Keith's eyes as he pulls back, watches his face as he pushes back in. They wind their arms around each other, get as close as they can. Keith's whining, eyes shining as he claws at his brother. He rocks into Keith, forgoing regular thrusts to keep him full. 

It's not long before Keith starts to get louder, keeps his face buried in his neck to try and muffle himself. Shiro gets a hand in his hair and pulls him out gently, to look at him. His cheeks are damp with tears and sweat beads on his forehead, lips and the corners of his mouth wet with spit. 

"Are you gonna come?" 

Keith nods, eyes closed.

"Good boy." Shiro murmurs, licks up the sweat on his neck. "Such a good baby brother for me, you gonna take my knot?" 

"Please Takashi, I want it. Let me have it."

"I'll give you everything baby. I love you."

"I love you too."

Fresh tears leaks from Keith's eyes as they come together, tightening almost painfully around Shiro's knot as it inflates. 

"Baby, a-are you okay?" 

Keith nuzzles into his neck, feet digging into his ass to keep him close.

"Keith, please, are you hurt?" 

"Feels good."

Shiro sighs happily as he rolls them back over, keeps his brother curled on his chest. 

"Thank you for helping me, Takashi."

"Any time at all bro."


End file.
